Guidewires are devices designed to facilitate insertion and placement of various tubular instruments such as catheters, stents, drains, cystoscopes, dilators and other items designed for penetration into various organs or body cavities to perform delivery or withdrawal of fluids, securing patency or access, removal of tissues for diagnostics or surgery, facilitating entry of other devices, etc.
In some procedures, guidewires are typically placed within the body at the desired location in advance, creating a convenient pathway for tubular instruments which are slid into their proper place over it. In other procedures, guidewires are inserted into the desired location together with the tubular instrument or device, e.g. a catheter, providing temporary stiffening needed for the insertion. Once the tubular instrument is in place, the guidewire may be removed and the instrument used for its primary purpose.
Guidewires are of various configurations, made from various materials and are made for various purposes. Their various kinds are sometimes also called Seldinger wires, introducers, mandrels, stylets etc. In the present specification, all such insertion devices for carrying tubular instruments to a desired body location are generally referred to as "guidewires".
In spite of their diverse shapes, sizes and uses, all guidewires devices have several problems in common (albeit, in various extent).
Each of these devices is required to penetrate through tight passages, which are often long and tortuous. This penetration is hindered by friction. The friction complicates the device placement, and may even cause injury to certain surfaces (e.g. tracheal, urethral or vascular wall). Therefore, the outer surfaces have to have low friction against contacting surfaces (e.g. vascular walls, inner walls of catheters or other instruments).
The low friction can be to some extent achieved by creating smooth, high quality surfaces (e.g. polished stainless steel, smooth plastic coatings, etc.). Since this is not always possible or sufficient, guidewires are often equipped with surface layers of various low-friction materials.
One such material widely used is poly(tetrafluoroethylene) (often known as TEFLON.RTM.) or similar fluoropolymers. It is used mostly on metallic guide-wires, either as a coating or as a sleeve pulled over the device.
For instance, U.S. Pat. No. 4,579,127 of Claus Haacke directed to a mandrel for hose type catheters and body probes, describes guidewires made from wound metal wires equipped with thin plastic coatings which follow the contours of the wire surfaces.
As another example, U.S. Pat. No. 4,811,743 of Robert C. Stevens describes a catheter guidewire consisting of a metal flexible core with spherical tip surrounded by sheath of tightly wound wire. The outside sheath surface is provided with a thin (&lt;0.001") Teflon.RTM. coating. Also, U.S. Pat. No. 4,826,485 of Theodore D. Johnson relates to a device for guiding tubings and describes a stylet for introducing, for example, gastric feeding tubes. The cable is made from metal or plastic wire, which forms the central portion of the stylet, which may be coated with an inert polymeric material such as medical grade Teflon.RTM.. The thickness of the coating is typically 0.002-0.004". Likewise, U.S. Pat. No. 4,834,709 of Robert D. Banning et al describes a preformable silicone catheter with a malleable stylet, comprising a malleable wire core and a plastic covering made of a polypropylene (preferred), polyethylene, Teflon.RTM., etc. The covering can be formed either as a coating, or from a pre-extruded plastic tubing which has larger lumen than the outer diameter of the wire so that it can be readily inserted.
Also, U.S. Pat. No. 4,867,173 of Gianni Leoni is directed to a steerable guidewire and describes a small-diameter guidewire for percutaneous translumenal coronary angioplasty (PTCA). The main core wire is said to be coated with a frictionless material such as Teflon.RTM.. Another U.S. Pat. No. 4,545,390, describes a guidewire with a Teflon.RTM.-coated main core wire.
Sometimes the plastic cover or coating has primary purpose of providing additional safety. For instance, U.S. Pat. No. 4,925,445 of Hidetoshi Sakamoto et al: "Guide wire for catheters" describes guidewire made from "super-elastic" memory titanium nickel or other metal alloys. It is provided with a plastic coating to increase its resistance against buckling. The coating can be made from an elastomeric or a composite material of a synthetic resin material including polyethylene, polyvinyl chloride, TEFLON.RTM., silicone rubber, etc.
U.S. Pat. No. 4,895,168 of James E. Machek entitled "Guidewire with movable core and external tubular safety cover" describes a guidewire with a wound wire casing covered by a plastic safety cover which is supposed to retain fragments of broken wire. This safety cover is preferably from heat-shrinkable TEFLON.RTM. tubing.
U.S. Pat. No. 4,884,579 of Erik T. Engelson: "Catheter Guide Wire" describes a guidewire with three sections of progressively decreasing rigidity. The central section has surface which is more lubricous than surfaces of adjacent proximal and distal sections. The intermediate section comprises a wirecore segment with flexible polymer covering which encases the intermediate core segment. The covering polymeric material provides appropriate flexibility to this section. The flexible polymer covering can be applied by spraying or dipping, or by a pre-formed tube which can be attached by heat shrinking over the core wire. This section has also low friction polymer surface. This can be achieved by using a covering made from a polymer which has a low friction in itself, such as TEFLON.RTM..
Alternatively, this polymer covering can be provided with a surface coating of a highly hydrophilic, low friction polymer, such as polyvinylpyrrolidine, polyethyleneoxide or poly(2-HEMA). Such a surface coating can be applied by spraying or dipping according to known methods.
This last example suggests the use of hydrophilic polymer surface coatings which have various advantages. For instance, hydrophilic coatings typically have lower wet friction than, e.g. Teflon.RTM.. They have lesser adhesion to tissue, to thrombus or to clot so that they are less prone to clogging, sticking to the wound, etc. Still another advantage is that the hydrophilic polymer layers can be used as a carrier for various water-soluble drugs, such as antibiotics.
Because of these advantages, hydrogel-coated surgical tubular devices are often suggested in the prior art. (For instance: U.S. Pat. No. 3,566,874 Francis E. Gould, Thomas H. Shepard: Catheter, U.S. Pat. No. 3,862,452 Otto Wichterle et al: Hydrogel Substitutes for Tubular Somatic Organs, U.S. Pat. No. 3,861,396 Vincent L. Vaillancourt et al: Drainage Tube, U.S. Pat. No. 4,026,296 Artur Stoy et al: Hydrophilic Surgical Tubular Device, U.S. Pat. No. 4,527,293 Eugene C. Eckstein et al: Hydrogel Surface of Urological Prothesis, U.S. Pat. No. 5,015,238 Donald D. Solomon et al: Expandable obturator and catheter assembly including same, to name only some.)
To this purpose, various hydrogel coating systems have been developed, based on polymerizable acrylic coatings (e.g. U.S. Pat. No. 3,695,921 Francis E. Gould, Thomas H. Shepard: Method of coating a catheter), on hydrophilic polyurethanes (e.g. U.S. Pat. No. 3,975,350 Donald E. Hudgin and Edgar A. Blair: Hydrophilic or Hydrogel Carrier Systems such as Coatings, Body Implants and other Articles), crosslinked poly(vinylpyrrolidine) (e.g. in U.S. Pat. No. 4,100,309 Michael J. Miclus et al: Coated substrate having a low coefficient of friction hydrophilic coating and a method of making the same; and U.S. Pat. No. 4,119,094 Michael J. Miclus et al: Coated substrate having a low coefficient of friction hydrophilic coating and a method of making the same etc.).
Such hydrophilic coatings can be applied also to guidewires. For instance, U.S. Pat. No. 4,798,593 of Peter Iwatschenko: Stiffening of probes describes mandrels for catheters etc. consisting of a wire element with coating of a biocompatible material of which at least the surface in hydrophilic. The coating may be applied by dipping or spraying. A specific hydrophilic polymer mentioned is gelatin softened, e.g., by glycerol.
In another example, U.S. Pat. No. 4,815,478 Maurice Buchbinder et al: "Steerable Guidewire with deflectable tip" describes a steerable guidewire consisting of a tubing (preferably flexible metal tubing) which provides for steering of a deflection wire, and a spring coil distal end. It is mentioned that it is advantageous to cover whole length of the guidewire, preferably including the tip, with a lubricious coating made from polymer such as Teflon.RTM. or a hydrogel.
The prior art hydrophilic coatings have certain specific problems:
1) There is often a problem to achieve a secure adhesion of the swellable hydrogel layer to the non-swellable substrates, such as crystalline hydrophobic polymer (TEFLON.RTM., polyolefin), or metal substrates. The main source of this problem is the volume change due to the swelling and the sharp transition between the swellable and non-swellable layer. A considerable shear stress can be thus generated in the interface which tends to separate the two materials. This may lead to delamination, peeling off and shedding of the resulting debris;
2) Difficult control of the surface thickness due to the swelling characteristics of the polymer;
3) Weakness in the polymer skin. The highly hydrophilic layers are soft and poorly resistant to scratching, abrasion or other mechanical damage. The denuded hydrophobic substrate can cause thrombus formation or other problems;
4) Increased production cost, particularly because the coating is applied to an otherwise finished, final device. Coating defects thus generate very expensive off-grades.
The present invention overcomes the above problems utilizing a heretofore untaught and unobvious device and method of production.